1. Field of the Invention
The present invention relates to a control system for controlling a hybrid vehicle having an internal combustion engine and an electric motor as separate propulsion sources, and more particularly to a control system for controlling a hybrid vehicle in regenerating electric energy with an electric motor.
2. Description of the Related Art
There have heretofore been known hybrid vehicles each having an internal combustion engine and an electric motor as separate propulsion sources. There has also been proposed a control system for controlling a hybrid vehicle to increase the regenerative efficiency of an electric motor when it operates in a regenerative mode at the time the hybrid vehicle is decelerating. For example, a control system disclosed in Japanese laid-open patent publication No. 8-112190 fully opens an electrically controlled throttle valve when the electric motor operates in the regenerative mode at the time the hybrid vehicle is decelerating. The amount of intake air supplied to the engine is thus made greater than when the throttle valve remains closed in the regenerative mode. Accordingly, a mechanical energy loss due to pumping losses of the engine is reduced, and the kinetic energy of the hybrid vehicle can efficiently be recovered as regenerated energy.
However, when the throttle valve is fully opened in the regenerative mode, a large amount of cold fresh air flows through the engine into its exhaust system. The introduced cold fresh air cools a three-way catalytic converter in the exhaust system, tending to impair emission characteristics of the three-way catalytic converter.